The Geometry Centerhttp://www.geom.uiuc.edu/
Center for the Computation and Visualization of Geometric Structures. This site no longer has live support, but there are lots of materials available on the site.
The Geometry Center at Science Uhttp://www.scienceu.com/geometry/
Interactive activities including tetrahedral puzzles and fractals.
The Geometry Center http://www.geom.uiuc.edu/
Center for the Computation and Visualization of Geometric Structures. This site no longer has live support, but there are lots of materials available on the site.
The Geometry Center at Science U http://www.scienceu.com/geometry/
Interactive activities including tetrahedral puzzles and fractals.
Building Math - Everest Trek and other exercises from Museum of Science Boston http://www.mos.org/educators/classroom_resources/curricula_and_research&d=2020
Learn Algebra by solving engineering challenges!